A stent graft is a medical device comprising a tube graft material supported by a metallic wire frame that may be used in the treatment of vascular diseases including aneurysms. Blood pressure within the diseased portion of the blood vessel can cause the aneurysm to rupture and hemorrhage. Stent-grafts can be used in the treatment of aneurysms, including thoracic aortic aneurysms and abdominal aortic aneurysms, by isolating the blood from the aneurysms. Typically, stents are deployed by placing them in a sheath of a delivery system and delivering the stent to the location where the aneurysm lies. After being deployed, the stent-graft expands and anchors onto healthy portions of the blood vessel on both ends adjoining the aneurysm. Once installed, blood flows through the tubular stent graft and the diseased portion of the blood vessel is isolated from the pressure of flowing blood.
A wide range of endovascular stent grafts have been developed that are adapted for temporary or permanent implantation within a body lumen including the abdominal aorta or thoracic aorta. These stent grafts provide uniquely beneficial structures that modify the mechanics of the targeted vessel wall. However, because conditions of weakened and diseased blood vessels differ greatly from patient to patient, existing stent-grafts have many drawbacks and may be restricted in their usefulness and applicability to certain procedures.
Many tubular stent grafts have been used in the treatment of aortic aneurysms, including abdominal aortic aneurysms and thoracic aortic aneurysms close to the aortic arch. The aortic arch comprises a sharp curve and disease and deformation of this blood vessel usually occurs close to the curved portion of the vessel. Because of the unique shape of the aortic arch, treatment of aneurysms in the aortic arch calls for flexibility and high performance in the stent-graft so that it can easily flex and adapt to the shape of the blood vessel. If the stent graft is not flexible, it cannot attach conformably to the wall of the blood vessel and may potentially kink. A kink in the stent graft will not only weaken the fixation of the stent graft to the vessel wall, but it may also raise the blood pressure within the graft due to the uneven or smaller inner diameter of the graft. High blood pressure in deployed stent grafts can lead to a higher flushing force of blood flow on the stent graft and a rise of the risk of stent graft migration as well. If the stent graft migrates within the arotic arch, it not only fails to isolate the blood from the aneurysm, but also may cover other branch vessels extending from the aorta. Covering the branch vessels in the aortic arch can lead to reduced blood flow to the rest of the body causing damage to nerves as well as vital organs of the patient and even death. Similar problems also exist when using bifurcated stent grafts in treatment of abdominal aortic aneurysms for the iliac arteries which also contain a sharp curve. Because of these issues, a more flexible stent graft is necessary in the treatment of aortic aneurysms.
The drawbacks in current stent graft designs also contribute to other complications in patients during and after stent graft treatment and placement. Endoleakage is a major complication of endovascular treatment of aortic aneurysms. Endoleakage is the persistence of blood flow into the aneurysm sac outside the stent graft. When endoleakage occurs, the aneurysm is not fully isolated from blood flow within the patient's blood vessel and risk of a potentially fatal rupture of the aneurysm remains. Most endoleakage occurs at the proximal portion of the stent graft once the stent graft is inserted into a patient. Improved deformability of the proximal end of stent grafts can prevent proximal endoleakage.
Present stent graft designs typically comprise an open stent that is not fully covered with graft material. Stents may comprise a series of waveforms or undulations having apexes. When aneurysm are located very close to an important branch vessel, the surgeon will position the proximal end of graft member with the open stent close to the distal end of the branch port and the open stent will cover the branch port in an effort to avoid occluding the branch. This method of stent graft placement does not occlude the branch port, improves the fixation of the stent graft to the vessel and strengthens the proximal radial supporting force of graft member.
While stent grafts with open stents have many advantages, use and placement of stent grafts having open stents is not without its risks. During the deployment of the stent graft when only the open stent is deployed from the deployment catheter sheath, the proximal apexes of the undulations of the open stent expand to their full diameter while the distal apexes of the undulations are still restricted. When the distal apexes are restricted, the expanded proximal apexes can overturn within the vessel. Overturning occurs when one or more complete undulations or one or more of the proximal apexes expand and turn backwards. During deployment of the stent graft, overturned apexes can stick to the wall of vessel. After full deployment of the stent graft, overturned undulations and apexes deform the proximal profile of the graft member and prevent the proximal end of the graft member from conformably attaching to the wall of vessel. A stent graft deformed in this manner increases the risk of proximal endoleakage as well as increases the risk of vessel rupture due to sticking of overturned apexes into the vessel wall.
One method used to reduce the potential of overturn of the apexes of the open stent, is to utilize longitudinally longer the open stents. Longer stents, however, not only cover the intended branch vessel, but also risk covering one more branch vessels not intended to be covered. Because stents are foreign objects within the human body, there is potential for the formation of blood clots known as thrombus on the surface of the stent wire. Since thrombus formation is unstable, there is a risk for it to be flushed away from the stent. When an open stent covers a branch, the thrombus may be flushed into the branch vessel and occlude some other smaller vessels of the branch. Occlusion of branch vessels can potentially be fatal to the patient. Less severe complications of open stents covering the port of the branch vessel include increased difficulty in future performance of minimally invasive surgery within the branch vessel due to vessel obstruction.
Other blood flow complications can occur during the deployment of bifurcated stents within patients. In bifurcated stent graft designs, two branches of varying lengths extended from a trunk portion of the graft. The longer branch is typically called the ipsilateral iliac branch and the shorter branch is typically called the contralateral iliac branch. During placement of a bifurcated stent graft, the distal part of ipsilateral branch is often positioned within the ipsilateral iliac artery and the entire contralateral iliac branch portion is positioned within the abdominal aorta. The abdominal aorta is the vessel that usually contains a large aneurysm sac or bubble. After the bifurcated stent graft is initially placed in the abdominal aorta, a branch stent graft extension positioned by a guide wire to be place in and joined to the bifurcated stent graft within the short branch, contralateral iliac branch.
The procedure placing the guiding wire into the contralateral iliac branch is difficult. The contralateral iliac branch typically has an inner diameter of about 10 to 14 mm. The abdominal aorta usually has an inner diameter of no more than 45 to 50 mm. Adding to the difficulties posed by the work space, blood flowing out from the short branch also works to prevent the guide wire from entering into the short branch. It often takes several attempts and 5 to 10 minutes to put the guide wire into the contralateral iliac branch, the short branch. This time accounts for ⅓ to ½ of the time a patient spends in surgery. What is needed is a stent and procedure that reduces the time a patient spends in surgery.
The disclosed invention provides for shortened surgery time and lessens the potential of injury to the patient from reduced blood supply during the operation.